ChemInform Abstract: Organocatalysis in the Stereoselective Bromohydrin Reaction of Alkenes (original) (raw)
Related papers
Catalytic, Asymmetric Halofunctionalization of Alkenes-A Critical Perspective
Angewandte Chemie International Edition, 2012
Despite the fact that halogenation of alkenes has been known for centuries, enantioselective variants of this reaction have only recently been developed. In the past three years, catalytic enantioselective versions of halofunctionalizations with the four common halogens have appeared and although important breakthroughs, they represent just the very beginnings of a nascent field. This Minireview provides a critical analysis of the challenges that accompany the development of general and highly enantioselective halofunctionalization reactions. Moreover, the focus herein, diverges from previous reviews of the field by identifying the various modes of catalysis and the different strategies implemented for asymmetric induction.
Recent advances in stereoselective bromofunctionalization of alkenes using N-bromoamide reagents
Chemical Communications, 2013
Bromination reactions have been made a lot more convenient since the invention of N-bromoamide reagents. These reagents are more easily handled when compared to molecular bromine. In comparison to other halogens, brominating reagents sit in between chlorine and iodine on the reactivity scale, giving them an advantage in some cases. Recently, several important advances in enantioselective bromofunctionalization of alkenes using such reagents have been reported. This article will highlight the challenges and methods to surmount these problems. In addition, this article will also show the use of N-bromoamide reagents in expanding the scope of diastereoselective bromofunctionalization of alkenes. Examples include bromine initiated cyclic ether cascades and novel multicomponent reactions (MCRs).
Molecules, 2012
The Brønsted-acidic ionic liquid 1-methyl-3-(4-sulfobutyl)imidazolium triflate [BMIM(SO 3 H)][OTf] was demonstrated to act efficiently as solvent and catalyst for the halogenation of activated organic compounds with N-halosuccinimides (NXS) under mild conditions with short reaction times. Methyl aryl ketones were converted into α-halo and α,α-dihaloketones, depending on the quantity of NXS used. Ketones with activated aromatic rings were selectively halogenated, however in some cases mixtures of α-halogenated ketone and ring-halogenated ketones were obtained. Activated aromatics were regioselectively ring halogenated to give mono-and dihalo-substituted products. The [BMIM(SO 3 H)][OTf] ionic liquid (IL-A) was successfully reused eight times in a representative monohalogenation reaction with no noticeable decrease in efficiency. An effective halogenation scale-up in this IL is also presented. The reactivity trend and the observed chemo-and regioselectiivities point to an ET process in these IL-promoted halofunctionalization reactions.
Deep Eutectic Solvent: An Efficient and Recyclable Catalyst for Synthesis of Thioethers
ChemistrySelect, 2017
An efficient nucleophilic aromatic substitution (S N Ar) reaction for CÀS bond formation using greener and reusable deep eutectic solvent (DES) has been described. A variety of thioethers are synthesized in impressive yields (88-98 %) by reacting various electron-deficient aryl/alkyl halides and thiols. This protocol is valid to aryl halides with diverse functional groups such as aldehydes, carboxylic acids, nitro and nitrile groups. The attractive features of this approach includes metal/ ligand free conditions, absence of organic solvents, short reaction time, easy isolation of products and simple work up procedure. This effective catalytic system is economically viable, environmentally benign and recyclable up to four cycles without significant loss in activity.
Novel regioselective aromatic chlorination via catalytic thiourea activation of N-chlorosuccinimide
Tetrahedron Letters, 2015
A metal and acid-free electrophilic aromatic chlorination methodology involving catalytic thiourea activation of N-chlorosuccinimide (NCS) is reported herein. Moderate yields and regioselectivities of chlorinated aromatics were obtained using a combination of 1.05-1.15 equivalents of NCS and 5 mol% of thiourea at room temperature in acetonitrile. A halogen bond between the sulfur atom of thiourea and the sigma-hole of the NCS chlorine atom is thought to enhance the electrophilic activity of the chlorine of NCS.
Journal of Organic Chemistry, 1983
The palladium-catalyzed reaction of a variety of halo ketones or halo aldehydes with acetonyl-and allyltin reagents gives cyclic ethers in good yields. Oxiranes, oxetanes, and tetrahydrofurans can be obtained under mild reaction conditions. The use of palladium catalyst containing chiral monophosphine ligands gave a small enantiomeric excess (up to 19%) of a chiral oxirane from an a-halo ketone. The allyl-and acetonyloxirane products tend to undergo further transformations in prolonged reactions: allyloxiranes rearrange to a-allyl aldehydes and acetonyloxiranes dehydrate to give substituted furans. The mechanism of the reaction appears to involve addition of the organotin ligand to the carbonyl, followed by palladium(11)-catalyzed cyclization of the tin alkoxides. Table I. Reaction of Halo Carbonyls with Acetonyl-and Allyltin Reagents Catalyzed by Benzylchlorobis(tripheny1phosphine balladium(I1) (1 l a Although the reaction of aldehydes and ketones with organometallic reagents to yield alcohols is relatively straight forward, the reaction of a-halo aldehydes with organometallics gives a variety of products. Grignard reagents react with a-chloro ketones,2 a-halo aldehyde^,^ and a,a-dihalo ketones4 to give carbonyl compounds by rearrangement of the intermediate magnesium alkoxide. The reaction of lithium cuprates with a-halo ketones yields products resulting from a-substitution or from copper enolate ~hemistry.~ The palladium-catalyzed reaction of a-halo ketones with allyltributylstannane to give mixtures of allyl-substituted oxiranes and their rearrangement products has been reported to take place under somewhat vigorous conditions (100 O C , 20 h).6 Because this reaction with tin reagents appeared to be a promising method for the generation of a carbon-carbon bond and the simultaneous formation of an oxirane, a study of the scope and utility of this reaction was undertaken. Results and Discussion The palladium-catalyzed reaction can be carried out under relatively mild conditions and is quite general for halo ketones or halo aldehydes with reactive organotins. Only organostannanes containing the readily transferable allyl and acetonyl groups give good yields of ethers (eq 1).